National Textile Center

Year 8 Proposal

Project No.: F97-D01

Competency: Fabrication

Scientific Study of Flock Materials and the Flocking Process

Project Team:

Leader: Yong K. Kim Expertise: Fiber Physics and Instrumentation

Email: ykim@umassd.edu Phone: 508-999-8452

Members: Armand F. Lewis, U Mass Dartmouth, Surface Chemistry

Objective:

  1. Develop a fundamental understanding of flock motion in electrostatic, gravitational and pneumatic force fields during the flocking process.
  2. Establish an understanding of textile based flock materials and processes from the standpoint of test procedures as they pertain to materials processing properties such as electrical conductivity and fiber motion.
  3. Develop a fundamental understanding of some of the functional properties for flocked materials such as functional and surface durability, coloration and color measurement.
  4. Understand fundamentals of controlling transport phenomena through flocked surfaces and assemblies.

Relevance to NTC Mission:

The U. S. flocking industry is far behind the European Union (EU) countries in their scientific and technical understanding of the flocking process. It is important that the U. S. flocking industries understand more fully this existing technology and expand upon it in areas more specific to U. S. flocking industry needs. These and related textile industries stand to benefit from this project in developing new areas of application of flocked materials. Over 40 US companies are in the flocking and flocking support industry who need a higher level of understanding of flock materials and their manufacturing processes. This project will enhance our knowledge base and assure the continuing viability of this expanding high value-added textile area.

State of the Art:

Flock quality is strongly influenced by the flock density on the finished flocked surface [Coldwell and Hersh 1978]. It is believed that flock density strongly depends on flock motion behavior in the electric field. The flock motion analyses found in the literature are based on simplified physical constraints in the flocking zone and charges on flock fibers. For example, Bershev derived the velocity profile of flock fibers under the assumption of a constant electrostatic field and without air drag force acting on fibers [Bershev 1977]. Other researchers relaxed the electrostatic field restriction by including the disturbance induced by a space charge on flock surfaces [Kleber and Schmidt 1992].

In our research work, we are proceeding to derive a more general mathematical model of flock motion under the following assumptions:

Flock fiber motion is completely described by the combination of the equation of motion, charge conservation (Gauss’s Law) and current continuity equations. These three equations are solved simultaneously together with proper boundary conditions in the flocking zone [Kim and Lewis 1998].

Very little has been reported on the direct optical observation of flock fiber particles in motion so that even the simplest theoretical model of flock motion can be verified. In our new work, we will employ a high speed CCD (charge coupled device) camera to analyze flock motion directly and verify our derived more general model for flock motion in an electrostatic field. This type of machine vision based measurement system will be extended to delineate a methodology which will directly measure flock density per unit area of substrate surface. Presently, flock density is measured indirectly using a mass balance weighing technique or employing non-optical sensors such as electrical capacitance. These indirect techniques are problematic due to reproducibility or applicability to off-line samples only. Our approach involves the counting of individually attached flock fibers using image analysis methods.

Textured fabrics including flocked surfaces appear differently when viewed from different angles. Flocked surface color measurement and matching are therefore much more complicated problems than the dyeing/coloration of traditional fabrics. There are no standardized procedures yet available which enables one to compare the color of a flocked surface with a color “standard” for color matching purposes. [Connelly Sr. 1997]. We are proposing to study fundamentals of color measurement and computer match prediction (CMP) of loose flock fibers and flocked fabric surfaces.

References

Bershev, E. N., “Developing the Physical Principles of Electrostatic Flocking Procedures,”

anonymous English translation of original Russian publication of the author, Moscow, 1977

Coldwell, R. L. and S. P. Hersh “ Influence of Processing Variables on the Properties of Flocked

Fibers” IEEE Trans. on Industrial Applications, Vol. 1A-14, #2 (1978)

Connelly Sr., R. L., “Good Sample Presentation: How to Get Color Measurement Results that

Make Sense”, Color Technology in the Textile Industry (2nd ed.), pp 78-83, AATCC, 1997

Kim, Yong K. and Armand F. Lewis, NTC Project F97-D01: Scientific Study of Flock Materials and the Flocking

Process, Annual Report, October 1998.

Kleber, W. and H-J Schmidt, “Computer Aided Optimizing of Electrical Fields for Flocking Operation”,

Proceedings of 11th International Flock Seminar, pp 10-1 to 10-24, Buedingen, Germany (1992)

Approach:

These specific points will be the overall focus of this research:

  1. Describe the behavior of short (dielectric) fibers in an electric field.
  2. Delineate the fiber materials’ properties that are important to carrying out an efficient and effective flocking process.
  3. Study the rheological and adhesion aspects of short fibrous particles impacting an uncured adhesive coating.
  4. Study the flocked materials and process parameters that lead to the creation of functionally durable flocked products.
  5. Develop a method for determining flock density by optical imaging techniques. This will replace unreliable or time-consuming mass-balance based procedures currently used in the flock industry.
  6. Probe coloration and color measurement and matching of flock materials and flocked surfaces.
  7. Describe and model transport phenomenon in flocked surfaces and assemblies.

This Year’s Goal:

  1. Develop a better understanding of flocking process variables that affect flock density and other quality parameters, which affect the quality of finished flocked materials.
  2. Delineate a methodology to directly measure flock density using machine-vision based instrumentation. This objective measurement procedure will establish the basis for in-process flocked material quality assurance. The current methods used in determining flock (surface attachment) density are time consuming and carried out off-line.
  3. Probe coloration and color measurement and matching of flock materials and flocked surfaces.

Outreach to Industry:

PI and team member’s previous industrial extension experience in flocked product development has created unique research capabilities and collaboration opportunities with industry. Overall, a better understanding of the adhesion process as it pertains to the high quality flock products would be beneficial to flock industry. Furthermore, it enables textile coating, non-conventional seaming and composite (laminated) fabric manufacturing sectors to be more competitive. It is possible that our approach will lead to the creation of novel sorptive surface concepts. This should broaden the application base for three dimensional flocked structures and consequently lead to the development of some novel forms of filtration materials.

New Resources Required:

The focus in Year 3 will be on the modeling of flock motion and its verification using high speed video instrumentation, optical flock density measurement, and color measurement and control on flocked surfaces. We have a high speed CCD based motion analyzer. New resources required are:

  1. Fiber optic based spectrophotometry instrumentation.
  2. Machine-vision based imaging system and compatible image analysis software.